Rotavirus vaccine keeps kids out of the hospital

NEW YORK (Reuters Health) - The number of young children hospitalized for severe diarrhea dropped sharply after the U.S. introduced rotavirus vaccination in 2006, a new government study finds.

Rotavirus is the top cause of severe gastroenteritis among children worldwide. Because infants and small children can quickly become dehydrated, the diarrhea and vomiting caused by the infection can be dangerous and even fatal.

In 2006, the U.S. licensed Merck's RotaTeq, or RV5, vaccine for immunizing infants against rotavirus.

In the new study, researchers at the Centers for Disease Control and Prevention (CDC) found that after the vaccine's introduction, hospitalizations for gastroenteritis among children younger than 5 fell substantially.

During the 2008 rotavirus season (January to June), the rate of such hospitalizations across 18 U.S. states was 45 percent lower than the rates for the years 2000 to 2006, the study found.

The typical hospitalization rate during those pre-vaccine years was 101 per 10,000 children younger than age 5. In 2008, the rate was 55 per 10,000 children, the researchers report in the Journal of Infectious Diseases.

The rotavirus vaccine is given in two or three doses, starting as early as six weeks of age, and should be completed by the time a baby is 8 months old. At the time of the 2008 rotavirus season, only about one-third of U.S. children younger than 2 had had at least one vaccine dose, and virtually no children older than 2 had been vaccinated.

But even with that limited vaccine coverage, hospitalizations dropped substantially -- including a 42 to 45 percent reduction among children who were between 2 and 6 years old, and too old to have been vaccinated.

The figures, Parashar said, "caught us somewhat by surprise -- a pleasant surprise."

He said the drop in hospitalizations among children in unvaccinated age groups reflect so-called "herd immunity" -- where vaccination, by reducing opportunities for disease transmission, indirectly benefits people who have not been immunized.

Parashar's team had data from only 18 U.S. states. But, extrapolating those figures to all states, they estimate that there were 55,500 hospitalizations for gastroenteritis among children younger than 5 during the 2008 rotavirus season. That compares with an estimated 101,600 per season between 2000 and 2006.

The findings come at a time of negative publicity for the rotavirus vaccine. In March, GlaxoSmithKline, maker of the second rotavirus vaccine to come on the market, announced that it had found bits of genetic material from a pig virus in its vaccine, called Rotarix.

Just last week, Merck said that it too had found "very low levels" of DNA from the virus in the RotaTeq vaccine. The virus, known as porcine circovirus (PVC), is not known to infect humans.

Last Friday, members of an advisory panel to the U.S. Food and Drug Administration (FDA) said that there is no evidence that PVC harms humans, and that the benefits of rotavirus vaccination outweigh the "theoretical" risks from PVC genetic material in the vaccines. The panel did not vote on any formal recommendations to the FDA.

Parashar said the current findings, along with those from past studies, "clearly show the tremendous impact of vaccination on severe diarrheal illness." Those benefits, he said, "have to be considered against the theoretical risks" associated with the PVC findings.

After Glaxo reported its findings, the FDA recommended that doctors temporarily stop using Rotarix while the agency investigates the issue further. No similar recommendation has been made regarding RotaTeq.

Experts are not sure how the PVC genetic material got into the vaccines, but one theory is that it was transferred from a pig-derived enzyme that is used in the vaccines' manufacturing process.